JP7779273B2 - Vehicle control device - Google Patents

Description

The present invention relates to a vehicle control device.

When a request to stop an engine that is running is made, the throttle valve closes, increasing pumping loss and stopping the engine's inertial rotation (see Patent Document 1).

Japanese Patent Application Publication No. 10-306739

When a request is made to stop a turbocharged engine during turbocharging operation, the turbocharger's compressor may continue to rotate by inertia even after the throttle valve is closed and the engine has stopped. In this case, even though the engine has stopped rotating, the compressor continues to rotate by inertia, which can cause air to be sucked into the gap between the throttle valve and the engine body, resulting in a pulsating noise.

The present invention therefore aims to provide a vehicle control device that suppresses the generation of pulsating noise when the engine is stopped during supercharged operation.

The above objective can be achieved by a vehicle control device equipped with an engine in which a throttle valve is located downstream of a turbocharger compressor in the intake direction, and a motor connected to the compressor or the engine, the vehicle control device comprising: a determination unit that determines whether a stop request has been made for the engine during turbocharging operation; and a stop control unit that, if a stop request has been made, controls the motor to stop the engine once the compressor rotation speed falls below a predetermined rotation speed.

The vehicle may include an acquisition unit that acquires boost pressure, the motor is connected to the engine and functions as a power source for driving the vehicle, and the stop control unit may control the motor so that the higher the boost pressure when the stop request is made, the longer the period from when the stop request is made until the engine stops rotating.

The stop control unit may control the absolute value of the negative torque of the motor to be smaller as the boost pressure increases, thereby slowing the rate at which the engine speed decreases.

The stop control unit may extend the standby time during which the negative torque of the motor is controlled to zero as the boost pressure increases.

The motor may be connected to the compressor, and the stop control unit may control the motor to reduce the rotation speed of the compressor to below the predetermined rotation speed before the engine stops rotating.

It is possible to provide a vehicle control device that suppresses the generation of pulsating noise when the engine stops during supercharging operation.

FIG. 1 is a schematic diagram of a hybrid vehicle. FIG. 2 is a schematic diagram of the engine. FIG. 3A is a flowchart illustrating stop control, and FIG. 3B is an example of a map that defines the rate of reduction in engine speed when an engine stop request is issued during supercharging operation. FIG. 4 is a timing chart illustrating the stop control in this embodiment. FIG. 5 is an example of a map that defines the waiting time when an engine stop request is issued during supercharging operation. FIG. 6 is a timing chart illustrating a first modified example of the stop control. FIG. 7 is a timing chart illustrating a second modified example of the stop control. FIG. 8 is a schematic diagram of a hybrid vehicle in which the third modified example of the stop control is carried out. FIG. 9 is a timing chart illustrating a third modified example of the stop control.

[General configuration of hybrid vehicle]
1 is a schematic diagram of a hybrid vehicle 1. In the hybrid vehicle 1, a clutch 30, a motor 40, and a transmission 50 are provided in this order in a power transmission path from an engine 10 to drive wheels 70. The engine 10 and the motor 40 are mounted as a drive source for running the hybrid vehicle 1. The engine 10 is, for example, a gasoline engine, but may also be a diesel engine. The transmission 50 and the left and right drive wheels 70 are connected via a differential 60. The transmission 50 includes a torque converter and an automatic transmission.

The clutch 30 is located between the engine 10 and the motor 40 on the power transmission path. When hydraulic pressure is supplied to the clutch 30, it switches from a disengaged state to an engaged state, connecting the power transmission between the engine 10 and the motor 40. When the hydraulic pressure supply is stopped, the clutch 30 switches to a disengaged state, cutting off the power transmission between the engine 10 and the motor 40.

The motor 40 is connected to the battery 90 via the PCU 80. The motor 40 functions as a motor that generates driving force for the vehicle in response to power supplied from the battery 90. The motor 40 also functions as a generator that generates regenerative power to charge the battery 90 in response to power transmission from the engine 10 and drive wheels 70. The power exchanged between the motor 40 and the battery 90 is regulated by the PCU 80.

The PCU 80 is controlled by the ECU 100, which will be described later, and converts the DC voltage from the battery 90 into AC voltage, or converts the AC voltage from the motor 40 into DC voltage. During powering operation, in which the motor 40 outputs torque, the PCU 80 converts the DC voltage from the battery 90 into AC voltage and adjusts the power supplied to the motor 40. This allows the PCU 80 to control the positive torque of the motor 40. During regenerative operation, in which the motor 40 generates power, the PCU 80 converts the AC voltage from the motor 40 into DC voltage and adjusts the regenerative power supplied to the battery 90. This allows the PCU 80 to control the negative torque of the motor. Note that torque in the direction that rotates the motor 40 forward is called positive torque, and torque in the direction that rotates the motor 40 reverse is called negative torque.

Hybrid vehicle 1 is provided with an ECU (Electronic Control Unit) 100 as the vehicle's control device. ECU 100 is an electronic control unit that includes a processing circuit that performs various calculations related to vehicle driving control, and memory that stores control programs and data. ECU 100 is an example of a control device for hybrid vehicle 1, and functionally realizes a determination unit, a stop control unit, and an acquisition unit, which will be described in detail below.

The ECU 100 drives the hybrid vehicle in either the motor driving mode or the hybrid driving mode. In the motor driving mode, the ECU 100 stops the engine 10, disengages the clutch 30, and drives the vehicle using power from the motor 40. In the hybrid driving mode, the clutch 30 is engaged and the vehicle drives using at least the power from the engine 10.

The driving mode is switched based on the torque required for the hybrid vehicle 1, which is calculated from the vehicle speed and accelerator pedal position. For example, if the required torque is less than the start threshold for starting the engine 10, a motor driving mode in which the engine 10 is stopped is selected to improve fuel efficiency. Therefore, if the required torque falls below the start threshold while driving in the hybrid driving mode, the engine 10 is stopped and the mode is switched to the motor driving mode, as described below.

[General configuration of the engine]
2 is a schematic diagram of the engine 10. The engine 10 includes an engine body 11, an intake passage 13, an exhaust passage 14, a turbocharger 15, an intercooler 16, a catalyst 17, a bypass passage 18, and a wastegate valve 19.

The engine body 11 is connected to an intake passage 13 and an exhaust passage 14. The intake passage 13 is provided with a compressor 15b of the supercharger 15. The exhaust passage 14 is provided with a turbine 15a of the supercharger 15. The turbine 15a and compressor 15b are coaxially connected by a shaft. The supercharger 15 supercharges the intake air to the engine body 11. The supercharger 15 also has an assist motor 15m that assists the rotation of the compressor 15b. The ECU 100 controls the drive of the assist motor 15m. Note that the compressor 15b is linked to the turbine 15a, so both the compressor 15b and the turbine 15a can be rotated by the assist motor 15m.

A bypass passage 18 that bypasses the turbine 15a is connected to the exhaust passage 14. A wastegate valve 19 that opens and closes the bypass passage 18 is provided in the bypass passage 18. The ECU 100 controls the opening degree of the wastegate valve 19. The distribution ratio between the flow rate of exhaust gas flowing through the bypass passage 18 and the flow rate of exhaust gas flowing through the turbine 15a is adjusted according to the opening degree of the wastegate valve 19. This adjusts the rotational driving force of the turbine 15a, adjusts the amount of air compressed by the compressor 15b, and adjusts the boost pressure of the engine 10.

An intercooler 16 is located downstream of the compressor 15b in the intake passage 13. Heat is exchanged between the refrigerant flowing through the intercooler 16 and the air passing through the intercooler 16, cooling the intake air. A throttle valve 13a is located downstream of the compressor 15b and intercooler 16 in the intake passage 13. The amount of intake air for the engine 10 is adjusted by adjusting the opening of the throttle valve 13a. The opening of the throttle valve 13a is controlled by the ECU 100 based on the accelerator pedal position. A catalyst 17 for purifying exhaust gas is located downstream of the turbine 15a in the exhaust passage 14.

The ECU 100 controls the operating state of the engine 10 based on detection signals from various sensors, including the air flow meter 22 and the boost pressure sensor 23. The air flow meter 22 detects the amount of intake air drawn into the intake passage 13. The boost pressure sensor 23 detects the pressure within the intake passage 13 downstream of the compressor 15b and upstream of the throttle valve 13a.

[Stop control]
FIG. 3A is a flowchart illustrating stop control. The ECU 100 determines whether or not there is an engine stop request during supercharged operation of the engine 10 (step S1). For example, such a stop is requested when switching from hybrid driving mode to motor driving mode during high-load operation. Step S1 is an example of processing executed by the determination unit. If the answer is No in step S1, this control is terminated. If the answer is Yes in step S1, the ECU 100 acquires the supercharging pressure based on the supercharging pressure sensor 23 (step S2). Step S2 is an example of processing executed by the acquisition unit. Next, the ECU 100 executes stop control (step S3). Step S3 is an example of processing executed by the stop control unit.

In the stop control of this embodiment, fuel supply to the engine 10 is stopped, the throttle valve 13a is closed, and the engine 10 is stopped after the compressor 15b has stopped rotating. In particular, the higher the boost pressure at the time the engine stop request is issued by the motor 40, the longer the period from the engine stop request until the engine 10 stops rotating. In this embodiment, reduction rate control is executed to control the rate at which the engine speed is reduced. Furthermore, in this embodiment, the stop control is achieved using the motor 40, which is the driving power source, and the assist motor 15m of the turbocharger 15 is not used.

Figure 3B is an example of a map that specifies the rate at which the engine speed decreases when an engine stop request is issued during supercharging operation. As shown in Figure 3B, the rate at which the engine speed decreases is specified to be slower the higher the supercharging pressure. ECU 100 refers to the map in Figure 3B and calculates the rate at which the engine speed decreases based on the supercharging pressure. Here, a high supercharging pressure indicates a high rotation speed of compressor 15b.

Figure 4 is a timing chart illustrating stop control in this embodiment. Figure 4 shows the transitions of boost pressure, engine speed, and motor negative torque. Motor negative torque is torque in the opposite direction to the rotation direction of the motor 40. Also, in Figure 4, a solid line indicates a case where boost pressure is low, and a dotted line indicates a case where boost pressure is high. First, the case where boost pressure is low will be described. Note that while the engine 10 is operating under supercharge, the clutch 30 is engaged. When an engine stop request is made and fuel supply is stopped, the motor negative torque is controlled to achieve the engine speed reduction rate calculated based on the map in Figure 3B. In other words, reduction rate control is executed. As a result, the engine speed and boost pressure begin to decrease (time t1).

When the engine speed drops below the stop permission speed, the reduction speed control is stopped, the motor negative torque is temporarily controlled to zero, and the engine speed remains approximately constant (time t2). After a predetermined time has passed, the motor negative torque is controlled to a predetermined value for stopping the engine 10 (time t3), and the engine speed drops to zero (time t4). Furthermore, between times t3 and t4, the boost pressure becomes zero, meaning that the engine 10 stops rotating after the compressor 15b stops rotating.

Next, we will explain what happens when the boost pressure is high. Whether the boost pressure is high or low, the motor negative torque is controlled to achieve the calculated rate of engine speed reduction, and the engine speed and boost pressure begin to decrease (time t1). Here, as shown in Figure 3B, the higher the boost pressure, the smaller the calculated rate of engine speed reduction. Therefore, the absolute value of the motor negative torque that achieves this rate of reduction is controlled to be smaller when the boost pressure is high than when the boost pressure is low. As a result, the engine speed decreases more gradually.

When the engine speed drops below the stop permission speed, the speed reduction control is stopped and the motor negative torque is temporarily controlled to zero (time t5). After a predetermined time has passed, the motor negative torque is controlled to a predetermined value for stopping (time t6), and the engine speed drops to zero (time t7). Furthermore, between times t6 and t7, the boost pressure becomes zero, meaning that the engine 10 stops rotating after the compressor 15b stops rotating.

As described above, whether the boost pressure is low or high, the engine 10 stops rotating after the compressor 15b stops rotating. This suppresses pulsating noise when the engine 10 is stopped. Furthermore, the higher the boost pressure, the longer it takes for the compressor 15b to stop rotating after a stop request is made, and therefore the longer the period from the stop request until the engine 10 stops rotating. This suppresses pulsating noise by stopping the engine 10 after the compressor 15b stops rotating, while avoiding the engine 10 continuing to rotate unnecessarily for a long period of time, which would cause discomfort to the driver.

The boost pressure at the time the engine stop request is issued may be detected by a boost pressure sensor, or may be estimated based on the detection value of a sensor that detects the rotation speed of the compressor 15b. This boost pressure may also be estimated based on the engine rotation speed, engine operating time, the opening and closing history of the wastegate valve 19, or other known methods. The boost pressure estimated as described above may also be corrected based on atmospheric pressure detected by an atmospheric pressure sensor or atmospheric pressure estimated based on position information.

In the above embodiment, the speed reduction control is performed when the engine speed is equal to or greater than the stop permission speed. However, this is not limited to this, and the speed reduction control may also be performed when the engine speed is below the stop permission speed. By performing the speed reduction control when the engine speed is low, the load on the motor 40 can be reduced. Note that the engine speed at which the speed reduction control is performed is preferably set to a speed that is away from the resonant speed at which the engine 10 resonates with other components.

[First Modification]
A first modified example of the stop control will be described. In the first modified example, standby time control is executed instead of the above-described speed reduction control. The standby time control is a control that ensures a time during which the engine speed is maintained substantially constant by controlling the motor negative torque to zero. In the first modified example, the stop control is realized using the motor 40, which is the traveling power source, and the assist motor 15m of the supercharger 15 is not used.

Figure 5 is an example of a map that specifies the standby time when an engine stop request is issued during supercharging operation. The standby time is the time during stop control during which the engine speed is maintained approximately constant by controlling the motor negative torque to zero. As shown in Figure 5, the standby time is specified to be longer the higher the supercharging pressure. ECU 100 calculates the standby time based on the supercharging pressure by referring to the map in Figure 5. Here, a high supercharging pressure indicates a high rotation speed of compressor 15b.

Figure 6 is a timing chart illustrating a first variant of stop control. Figure 6 corresponds to Figure 4. First, we will explain the case where the boost pressure is low. When an engine stop request is made and fuel supply is stopped, the motor negative torque is controlled to a predetermined value, and the engine speed and boost pressure begin to decrease (time t1).

When the engine speed drops below the stop permission speed, standby time control is executed, the motor negative torque is controlled to zero, and the engine speed is maintained approximately constant (time t2). After the standby time calculated based on the map described above has elapsed, standby time control is stopped, the motor negative torque is controlled to a predetermined value (time t3), and the engine speed drops to zero (time t4). In this case, too, the engine 10 stops rotating after the compressor 15b stops rotating.

Next, we will explain what happens when the boost pressure is high. As with the case where the boost pressure is low, the motor negative torque is controlled to a predetermined value, and the engine speed and boost pressure begin to decrease (time t1). Here, the motor negative torque is the same whether the boost pressure is high or low. Therefore, it takes longer for the engine speed to decrease below the stop permission speed when the boost pressure is high than when the boost pressure is low. Once the engine speed decreases below the stop permission speed, standby time control is executed, and the engine speed is maintained approximately constant (time t4). Here, as shown in Figure 5, the higher the boost pressure, the longer the calculated standby time. Therefore, after a standby time longer than when the boost pressure is low, the standby time control is stopped, the motor negative torque is controlled to a predetermined value (time t5), and the engine speed decreases to zero (time t6). In this case, the engine 10 also stops rotating after the compressor 15b stops rotating.

In the example shown in Figure 6, standby time control is executed when the engine speed reaches a speed closer to the stop permission speed than 0, but this is not limited to this. For example, standby time control may be executed when the engine speed reaches a predetermined speed closer to 0 than the stop permission speed. In this case, too, it is preferable to set the engine speed at which standby time control is executed to a speed that is away from the resonant speed at which the engine 10 resonates with other components. Furthermore, the above embodiment and the first modified example may be executed simultaneously.

[Second Modification]
A second modified example of the stop control will be described. In the second modified example, compressor deceleration control is executed to decelerate the rotation of the compressor 15b using the assist motor 15m. The compressor deceleration control is a control to decelerate the rotation of the compressor 15b by increasing the torque of the assist motor 15m in the direction opposite to the rotation direction of the compressor 15b.

Figure 7 is a timing chart illustrating a second variant of stop control. Figure 7 corresponds to Figure 4. As the motor negative torque is controlled to a predetermined value, the engine speed begins to decrease, and compressor deceleration control begins to significantly decrease the boost pressure (time t1). When the engine speed decreases below the stop permission speed, standby time control is executed, the motor negative torque is controlled to zero, and the engine speed is maintained approximately constant (time t2). Even at this time, compressor deceleration control continues, the rotation of compressor 15b stops, and the boost pressure becomes zero (time t3). After a predetermined time has elapsed, the motor negative torque is controlled to a predetermined value for stopping engine 10 (time t4), and the engine speed decreases to zero (time t5).

As described above, the rotation of the compressor 15b can be stopped early using the assist motor 15m. This allows the rotation of the engine 10 to be stopped early after the compressor 15b has stopped. This prevents the driver from feeling uncomfortable due to the engine 10 not stopping.

Unlike the present embodiment and the first modification described above, the second modification does not use a motor 40. Therefore, the second modification can also be implemented in engine vehicles that have only an engine as a driving power source. Note that in hybrid vehicles, the second modification and at least one of the above-described embodiment and the first modification may be implemented simultaneously.

[Third Modification]
8 is a schematic diagram of a hybrid vehicle 1a in which a third modified example of the stop control is implemented. The hybrid vehicle 1a includes an engine 10, a power split device 30a, a first motor 41, a second motor 42, a transmission mechanism 60a, drive wheels 70, a PCU 80a, a battery 90, and an ECU 100a. The first motor 41 and the second motor 42 are connected to the battery 90 via the PCU 80a. The first motor 41 and the second motor 42 function as motors that generate driving force for the vehicle in response to power supplied from the battery 90, and also function as generators that generate regenerative power to charge the battery 90 in response to power transmitted from the engine 10 and the drive wheels 70. The power exchanged between the first motor 41, the second motor 42, and the battery 90 is adjusted by the PCU 80a.

The power split mechanism 30a mechanically connects the crankshaft of the engine 10, the rotating shaft of the first motor 41, and the output shaft of the power split mechanism 30a. The power split mechanism 30a is, for example, a planetary gear mechanism equipped with a sun gear, planetary carrier, pinion gear, and ring gear. The output shaft of the power split mechanism 30a is connected to a transmission mechanism 60a. The rotating shaft of the second motor 42 is also connected to the transmission mechanism 60a. The driving forces of the engine 10, first motor 41, and second motor 42 are transmitted to the drive wheels 70 via the transmission mechanism 51.

Figure 9 is a timing chart illustrating a third variant of stop control. Figure 9 shows the trends in boost pressure, engine speed, first motor negative torque, and second motor negative torque. Figure 9 corresponds to Figure 4. First, we will explain the case where boost pressure is low. When an engine stop request is made and fuel supply is stopped, the negative torque of the first motor 41 and the second motor 42 is controlled to achieve the engine speed reduction rate calculated based on the map in Figure 3B. In other words, reduction rate control is executed. As a result, the engine speed and boost pressure begin to decrease (time t1).

When the engine speed drops below the stop permission speed, the reduction speed control is stopped, the negative torque of the first motor 41 and the second motor 42 is temporarily controlled to zero, and the engine speed remains approximately constant (time t2). After a predetermined time has passed, the negative torque of the first motor 41 and the second motor 42 is controlled to a predetermined value for stopping the engine 10 (time t3), and the engine speed drops to zero (time t4). Furthermore, between times t3 and t4, the rotation of the compressor 15b stops, and then the rotation of the engine 10 stops.

Whether the boost pressure is high or low, the negative torque of the first motor 41 and the second motor 42 is controlled to achieve the calculated rate of decrease in engine speed, and the engine speed and boost pressure begin to decrease (time t1). Here, to achieve the rate of decrease shown in Figure 3B, the absolute value of the negative torque of the first motor 41 and the second motor 42 is controlled to be smaller when the boost pressure is high than when it is low. As a result, the engine speed decreases gradually.

When the engine speed drops below the stop permission speed, the reduction speed control is stopped and the negative torque of the first motor 41 and the second motor 42 is temporarily controlled to zero (time t5). After a predetermined time has passed, the negative torque of the first motor 41 and the second motor 42 is controlled to a predetermined value for stopping (time t6), and the engine speed drops to zero (time t7). Furthermore, between times t6 and t7, the compressor 15b stops rotating, and then the engine 10 stops rotating.

Even in a hybrid vehicle 1a equipped with two motors, a first motor 41 and a second motor 42, the engine 10 can be stopped after the compressor 15b has stopped rotating. This suppresses pulsating noise when the engine 10 is stopped. Note that at least one of the first and second variants and the third variant may be implemented simultaneously.

In the above embodiment and modified example, the engine 10 is stopped after the compressor 15b stops rotating, but this is not limiting. For example, the engine 10 may be stopped when the rotation speed of the compressor 15b falls below a predetermined rotation speed at which pulsating noise is not a problem. In other words, the engine 10 may be stopped even when the compressor 15b is rotating, as long as the pulsating noise is within a range that is not a problem. The predetermined rotation speed is set to the maximum rotation speed of the compressor 15b at which pulsating noise does not become a problem even when the engine 10 stops rotating. The boost pressure corresponding to this predetermined rotation speed is determined in advance based on experimental results and stored in the memory of the ECU 100. Therefore, the ECU 100 may stop the engine 10 when the boost pressure falls below the boost pressure corresponding to the predetermined rotation speed.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to these specific embodiments, and various modifications and variations are possible within the scope of the gist of the present invention as set forth in the claims.

REFERENCE SIGNS LIST 1 Hybrid vehicle 10 Engine 15 Supercharger 15b Compressor 15m Assist motor 40 Motor 100 ECU (control device, determination unit, stop control unit, acquisition unit)

Claims (2)

A control device for a vehicle including an engine in which a throttle valve is disposed downstream of a compressor of a turbocharger in an intake air direction, and a motor connected to the compressor or the engine,
a determination unit that determines whether or not a stop request is issued for the engine during supercharging operation;
a stop control unit that controls the motor when there is a stop request, thereby stopping the rotation of the engine after the rotation speed of the compressor becomes equal to or lower than a predetermined rotation speed;
an acquisition unit that acquires a supercharging pressure,
the motor is connected to the engine and functions as a power source for driving the vehicle;
the stop control unit controls the motor so that the higher the supercharging pressure when the stop request is made, the longer the period from when the stop request is made until the rotation of the engine is stopped;
The stop control unit controls the motor so that the absolute value of the negative torque becomes smaller as the supercharging pressure becomes higher, thereby slowing down the rate at which the engine speed decreases . the motor is coupled to the compressor;
2. The vehicle control device according to claim 1 , wherein the stop control unit controls the motor to reduce the rotation speed of the compressor to equal to or lower than the predetermined rotation speed before the rotation of the engine stops.